Alternator size

Slappp

CarAudio.com Newbie
I need help choosing an alternator size. Is there a formula that helps determine what is right for your car?

I have a 99 LexuS LS400 with an oem 100A alternator. The mono amp I plan on running for subs is a 3000W amp which manufacturer says has a max music consumption of 190A. Will a 320A alternator (along with big 3 of course) be enough to run this amp without a secondary battery? I don't play music with my car off. I have no idea if an alternator that size is enough or if it's unnecessarily big.
 
Are you trying to avoid a dead battery or headlight dimming?

Alternators prevent dead batteries. Batteries and capacitors prevent headlight dimming.
 
What amp? "max music consumption of 190A" sound odd to me. What size fuse/s does the amp have?
Really depends on your definition of "music". I rarely opened 80A fuses running 1200W amps.

Still though, I wouldn't count on just a high output alternator keeping up with a 3000W amp if you like playing bass heavy music. Would possibly be a good application for supercap bank though.
 
What amp? "max music consumption of 190A" sound odd to me. What size fuse/s does the amp have?
Taramps Smart Bass 3. On their website they gave that figure in the specifications.
Really depends on your definition of "music". I rarely opened 80A fuses running 1200W amps.

Still though, I wouldn't count on just a high output alternator keeping up with a 3000W amp if you like playing bass heavy music. Would possibly be a good application for supercap bank though.
Yea Bass heavy is the type of music I will play. Have not bought the amp yet so still need to figure what size fuse. Sounds like I need to be researching a super cap bank as well. Any recommendations for a 3000W amp?
 
Sounds like I need to be researching a super cap bank as well.
Second battery would be simpler if you can deal with the space and weight. The Maxwell brand supercaps may also do the job for you assuming your alternator makes enough current to run that amp but will only need a second's worth of reserve to keep the amp properly fed while the alternator loads down as needed.

Search the site, there's likely someone using those supercaps and there's definitely pre-made bus bars and such on the market for our applications.
 
Second battery would be simpler if you can deal with the space and weight. The Maxwell brand supercaps may also do the job for you assuming your alternator makes enough current to run that amp but will only need a second's worth of reserve to keep the amp properly fed while the alternator loads down as needed.

Search the site, there's likely someone using those supercaps and there's definitely pre-made bus bars and such on the market for our applications.
I've been looking into an IOXUS ultra cap. Any experience with those?
 
Taramps Smart Bass 3. On their website they gave that figure in the specifications.

Yea Bass heavy is the type of music I will play. Have not bought the amp yet so still need to figure what size fuse. Sounds like I need to be researching a super cap bank as well. Any recommendations for a 3000W amp?
40ah of LiFePO4 (lithium secondary battery) would solve all your problems.
 
I need help choosing an alternator size. Is there a formula that helps determine what is right for your car?

I have a 99 LexuS LS400 with an oem 100A alternator. The mono amp I plan on running for subs is a 3000W amp which manufacturer says has a max music consumption of 190A. Will a 320A alternator (along with big 3 of course) be enough to run this amp without a secondary battery? I don't play music with my car off. I have no idea if an alternator that size is enough or if it's unnecessarily big.
That Alt and The largest AGM with another matching should be just fine. vehicle should be running at all times to maintain proper voltage when playing the stereo. It takes power to make power... Supply for the demand
 
3000w / 14.4v = 208 amps.
208 amps / .85 % (amp efficiency) = 245 amps is what you should expect your amp to draw. 190 seems underrated.

100 amps for the factory vehicle is probably a little oversized on what you actually use, but that's your fuel injection, computer, headlights, turn signals, brake lights, gauges, your two biggest are electric fans and Air conditioner.

320a sounds about right size for your alt, if that's what your alt will put out. If you haven't bought the alt yet, you want to know two things. Amps at (or near) idle, and what rpm for full output. If a manufacturer can't give you both, then keep looking. A cheap 320 alt will do less at idle than your factory 100, and won't do max output until over 3K rpms, (which you will never be cruising at). A quality alt will do more than half at idle, and full somewhere around 2K. They will also be able to give you an actual curve of your actual alternator. You should know those numbers, and where your cruising rpm is, before buying.

You're clearly going to need an alt to keep that going. You will probably need a battery too, but if you do the alt, and your lights dim as it hits, (and you have done the big 3, and your electrical is good), then your battery is too small, (too small of an output). If you crank it up, and your voltage drops after 30minutes to an hour, then your alt is too small.


A battery is a storage bank. If you only listen to your music when your engine is running, (and your alt is charging), then you only need enough to keep it going. If you play your music with the engine off, and need it to play for a longer time, then you would need another battery so you have a reserve / larger storage bank. You probably need a new battery, but what you don't want is to buy an alternator, and it's just too small, and then you need another one. There is no reason you can't go bigger if that's an option, but your numbers sound like they work if the RPMs will keep that alt charging at the rate you need it to.
 
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SLAPP, Hello. In the industry the rule of thumb is use a1 farad capacitor per 1000 watts. However if your amp really puts out 3000 watts of power continuously, you will need 2 of the 1 farad caps for each 1000 watts to keep up with the power draw of the Bass notes. What; brand of amp are you using? Linear Power, Hifonics, Rockford Fosgate, Pyramid, Stillwater Designs? What size speakers are you driving with this big amp? 6 15inch in a box? Is the amp 2, or 4 channel? is it bridgeable? You may want to use active crossover(s) between the head unit and the amp to control the frequency. How big is the box you are using for the subwoofers? If your amp is 3000 watts divided by 4 channels RMS it is a huge amp and even bigger if only a 2 channel. The headroom of the amp may be 3000 watts that will allow an occasional peak of the max rated power of each channel in watts per channel for a 4 channel, or watts per channel for a 2 channel amp. If you are bridging a 2 channel amp. The actual formula is: Power (W) = (Volts x Volts) or P = V^2 / R for example: A 50 watt/channel amp with a resistance of 4 ohms drawing 14.4 VDC (volts in DC current) with one two channel amp at peak will achieve: (14.4 VDC x 14.4 VDC) / 4 = 51.84 watts for each channel on the amp. Also keep in mind that a 4 ohm 2 channel amp in bridged mode will more than likely become 4 times the power in a 2 ohm load on the amp. That creates more heat. (Another calculation)
 
SLAPP, Hello. In the industry the rule of thumb is use a1 farad capacitor per 1000 watts. However if your amp really puts out 3000 watts of power continuously, you will need 2 of the 1 farad caps for each 1000 watts to keep up with the power draw of the Bass notes. What; brand of amp are you using? Linear Power, Hifonics, Rockford Fosgate, Pyramid, Stillwater Designs? What size speakers are you driving with this big amp? 6 15inch in a box? Is the amp 2, or 4 channel? is it bridgeable? You may want to use active crossover(s) between the head unit and the amp to control the frequency. How big is the box you are using for the subwoofers? If your amp is 3000 watts divided by 4 channels RMS it is a huge amp and even bigger if only a 2 channel. The headroom of the amp may be 3000 watts that will allow an occasional peak of the max rated power of each channel in watts per channel for a 4 channel, or watts per channel for a 2 channel amp. If you are bridging a 2 channel amp. The actual formula is: Power (W) = (Volts x Volts) or P = V^2 / R for example: A 50 watt/channel amp with a resistance of 4 ohms drawing 14.4 VDC (volts in DC current) with one two channel amp at peak will achieve: (14.4 VDC x 14.4 VDC) / 4 = 51.84 watts for each channel on the amp. Also keep in mind that a 4 ohm 2 channel amp in bridged mode will more than likely become 4 times the power in a 2 ohm load on the amp. That creates more heat. (Another calculation)
No, just no. None of this is correct. The math has already been done, the solution has already been given, please don't bump posts with incorrect information like this.

Matt


Edit:

I'm going to take a minute to apologize and try to steer you in the right direction for the future. Audio has evolved alot and continues to evolve.

The 1-5 farad caps have proven to do nothing more than be a waste of money, you really need large caps called "supercaps" to have any positive influence. Maxwell is a common name-brand supercaps used now.

The simplest way to calculate current demand for a car stereo is to follow this general structure:
1. Identify factory alt amperage(100a in this case)

2. Identify current required for added stereo using this formula: rated wattage of amp(s) divided by 12. Since this is a 3000w amp, you would divide 3000 by 12 and get 250a. This isn't an exact method, and some people prefer to use slightly different formulas, but this formula has worked well for me.

3. Identify available alternator or battery upgrades to support the additional current draw. Batteries add reserve capacity once you exceed the alternators output, alternators add extra power before you hit reserve.

In this case we need to add an additional 250a of power for this situation. Everyone has their own method for "best" making up this difference, so I'm not going to go into the specifics here.

4. Install everything and enjoy your music.
 
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